1. Field of the Invention
This invention relates to a fuse element used in integrated circuit devices, and more particularly to the structure of a fuse link to be deleted by laser radiation. The invention further relates to the method of making the fuse link.
2. Description of Related Art
Fuses are used in semiconductor chips to provide redundancy, electrical chip identification, and customization of function. For designs having three (or more) layers of wiring, the fuses are typically formed from a segment of one of the wiring layers, usually the last metal layer or the penultimate metal layer, i.e., the xe2x80x9clast metal minus onexe2x80x9d wiring layer.
Fusing is the deletion of a segment of metal fuse line. One standard way this can be accomplished is by exposing the segment to a short, high intensity pulse of light energy from a laser, typically having infrared wavelength. The metal line absorbs the laser light energy, melts, and ruptures, disrupting line continuity and causing high electrical resistance, i.e., an open line. A sensing circuit may be used to detect this fuse segment resistance. The technique of laser fuse deleting or trimming has been widely used both in memory and logic integrated circuit fabrication.
Fuse fabrication has taken advantage of the energy transfer from infrared laser light. Lasers allow for precise selection and illumination of integrate circuit segments. Using this technology to delete fuse links facilitates IC fabrication. For example, in U.S. Pat. No. 5,608,257 issued to Lee, et al., on Mar. 4, 1997, entitled, xe2x80x9cFUSE ELEMENT FOR EFFECTIVE LASER BLOW IN AN INTEGRATED CIRCUIT DEVICE,xe2x80x9d a fuse structure is taught that increases absorption of the laser energy, having a melt-away elongated fuse link joining two segments of an interconnecting line, a plurality of fins integral and coplanar to the fuse link such that each of the fins transversally extends away from the fuse link, and a reflecting plate positioned underneath the fuse link to reflect the applied laser energy. By adding structure to the fuse link (fins and reflective pad), the fuse is made more absorptive of the infrared laser energy. Thus, minimizing the incident energy required to delete the fuse.
In some circuits, such as CMOS logic circuits, the fuses are located in arrays close together. This close proximity of fuses provides technical challenges when infrared laser light is applied to blow a particular fuse. Spurious reflections of beam energy and the explosive effects of fuse blowing can adversely affect any element adjacent to the blown fuse link.
In U.S. Pat. No. 5,420,455, issued to Gilmour, et al., on May 30, 1995, entitled, xe2x80x9cARRAY FUSE DAMAGE PROTECTION DEVICES AND FABRICATION METHOD,xe2x80x9d an approach to limit these reflections is taught by adding non-frangible, high melting point barriers, positioned adjacent to the fuse structures, to prevent both the beam energy and the effects of fuse blowing to reach or affect any adjacent element in the circuit. These barriers act as protective shields for adjacent structures.
Inter-element dimensions in these arrays remain an essential characteristic. However, technology advances require that these dimensions continue to get smaller.
As the reflectivity, mass, and melting temperature of the fuse link metal increases, higher laser energies and longer (or multiple) laser pulses are required to accomplish deletion of the fusible link. These higher energies and longer pulses provide sufficient energy to adjacent and underlying structures, e.g., silicon under the fuse area, to cause severe damage to the interlayer dielectric oxide and adjacent fuse wiring. Additionally, infrared laser deletion of copper fuses is more difficult due to the high reflectivity of copper, especially in the 1.0 to 1.4 xcexcm wavelength range that is commonly available in laser fuser tools.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a fusible link structure and method for making the same that allows for deletion of fuses having high reflective, high melting point conductors, when exposed to an infrared laser energy beam at energy levels lower than that required in the current state of the art for blowing fuse links.
It is another object of the present invention to provide a fusible link with increased absorption to infrared laser light.
A further object of the invention is to provide a fusible link that allows for close placement of fuse arrays without structural damage to adjacent structures during fuse deletion, and without the need for protective barriers between adjacent structures.
Still other advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a conductor having a given conductivity characteristic that can be substantially altered by radiation, comprising an electrical conductor having a first layer of a first material that is substantially insensitive to the radiation, and a second layer of a second material that is sensitive to radiation. The sensitivity of the second material is to radiation emitted from a laser in an infrared energy spectrum. The first material is a primary electrical conductor and the second material is an electrical conductor of a composition such that when combined with the primary electrical conductor provides for a high infrared energy absorbing structure.
The first material is copper and the second material is tungsten or a titanium-tungsten composition. The infrared energy spectrum comprises energy having wavelengths in the range of 1.0 to 1.4 xcexcm. The first layer of the first material is greater than or equal to 500 angstroms in thickness, and the second layer of the second material is greater than or equal to 500 angstroms in thickness.
In a second aspect, the invention is directed to a fusible link that can be selectively opened by laser radiation at a predetermined wavelength, comprising a first conductor that is not substantially absorptive for the radiation at the predetermined wavelength, and a second conductor that is substantially absorptive for the radiation at the predetermined wavelength.
In a third aspect, the invention is directed to a fusible link having a given conductivity characteristic that can be substantially altered by infrared radiation, comprising a first layer of copper, and a second metal layer, wherein the second metal layer is tungsten or titanium-tungsten that is sensitive to the infrared radiation. The infrared radiation comprises energy in the range of 1.0 to 1.4 xcexcm wavelengths.
In a fourth aspect, the invention is directed to a method for making a conductor on a semiconductor substrate sensitive to incident infrared radiation, comprising the steps of: a) forming a damascene copper wiring underlayer on the semiconductor substrate; b) recessing the copper underlayer to a first predetermined thickness; c) depositing a metal overlayer at a second predetermined thickness on the copper underlayer, having optical properties for absorbing the infrared radiation at an amount greater than the copper underlayer; and, d) polishing the metal overlayer to remove extraneous metal, and having the metal overlayer cover the copper underlayer in its entirety.
The method may further comprise the step of e) completing integrated circuit fabrication or other passivation sequence.
The method step (b), recessing the copper underlayer, further comprises using a blanket wet etch.
In the method step (c), the metal overlayer is tungsten or titanium-tungsten, and depositing the metal overlayer, further comprises using a chemical vapor deposition technique or a sputtering technique. The blanket wet etch comprises ammonium persulfate.
In a fifth aspect, the invention is directed to a method for making a conductor on a semiconductor substrate sensitive to incident infrared radiation, comprising the steps of: a) providing the semiconductor substrate having a surface with integrated circuit device structures thereon; b) applying a silicon oxide layer over the substrate surface and the integrated circuit device structures; c) applying a first photoresist mask to the silicon oxide layer to outline a fuse link line; d) imaging and etching the first photoresist mask to form the fuse link line in the silicon oxide layer at a first predetermined depth; e) applying a second photoresist mask to the silicon oxide layer; f) imaging and etching the second photoresist mask to form vias; g) stripping the second photoresist mask and depositing within the fuse link line and the vias a first conductive material; h) recessing the first conductive material to a second predetermined depth; i) depositing within the recessed area a second material, such that when the second material is combined with the first conductive material the combination is capable of absorbing more of the infrared radiation than the first conducting material alone; and, j) planarizing and applying a protective passivation layer over the fuse link line.
Etching the first photoresist mask to a first predetermined depth, comprises etching to a depth greater than or equal to 500 angstroms.
In step (g), depositing a first conductive material, comprises depositing copper metal. In step (h), the second predetermined depth is greater than or equal to 500 angstroms. Additionally, in step (i) the second material comprises a tungsten composition.
In a sixth aspect, the invention is directed to a method for selectively making a fuse on a conductor of a semiconductor substrate, having a sensitivity to incident infrared radiation, comprising the steps of: a) providing the semiconductor substrate having a surface with integrated circuit device structures thereon; b) applying a silicon oxide layer over the substrate surface and the integrated circuit device structures; c) applying a first photoresist mask to the silicon oxide layer to outline a fuse link line; d) imaging and etching the first photoresist mask to form the fuse link line in the silicon oxide layer at a first predetermined depth; e) applying a second photoresist mask to the silicon oxide layer; f) imaging and etching the second photoresist mask to form vias; g) stripping the second photoresist mask and depositing within the fuse link line and the vias a first conductive material; h) applying a third photoresist mask over the fuse link line and the vias to form a recessed area of a second predetermined depth for the fuse; i) imaging and etching the third photoresist mask in the fuse area; j) depositing within the recessed area a second material, such that when the second material is combined with the first conductive material the combination is capable of absorbing more of the infrared radiation than the first conducting material alone; and, k) planarizing and applying a protective passivation layer over the fuse link line.
In a seventh aspect, the invention is directed to a method for selectively making a fusible link on a semiconductor substrate, the link sensitive to incident infrared radiation, comprising the steps of: a) forming a damascene copper wiring underlayer on the semiconductor substrate; b) applying and imaging a photoresist mask to limit portions of the copper wiring underlayer for enhanced sensitivity to the incident infrared radiation; c) recessing the portions of the copper underlayer to a first predetermined thickness; d) removing the photoresist mask; e) depositing a titanium-tungsten metal overlayer at a second predetermined thickness on the copper wiring underlayer, having optical properties for absorbing the infrared radiation at an amount greater than the copper underlayer; and, f) polishing the metal overlayer to remove extraneous metal, and having the titanium-tungsten metal overlayer cover the copper underlayer in its entirety.
In an eighth aspect the invention is directed to a fuse structure for use with IC designs comprising an overlayer and an underlayer wiring, defined using a damascene process, the wiring made from metals which are highly reflective to energies in the 1.0 xcexcm to 1.4 xcexcm wavelength range. The thickness and optical properties of the overlayer maximizes the absorption of infrared energy by the structure. The underlayer is a copper prime conductor, and the overlayer acts as a diffusion barrier. The overlayer may be a diffusion barrier for Sn.